Disk film optical measurement system

ABSTRACT

A method and apparatus for inspecting a reflective surface, or material on such surface, such as lubricant and planarizing layers on a magnetic media storage disk. A beam of controlled polarization impinges obliquely at a spot in the plane of the disk. A collector such as an integrating sphere is spaced away from the disk and has an opening oriented to catch the oblique specular reflectance from the surface. Preferably the opening is substantially larger than the beam, so that disk run out does not send the beam astray or defeat its measurement, and the oblique beam is aimed at an angle lying between the Brewster angle of the lubricant and that of the adjacent layer. A temperature-controlled laser diode with constant-current driver provides a beam that is free of wavelength hops and amplitude changes, making beam aiming repeatable and allowing point-by-point comparisons of the detected reflectance. The disk spins at high speeds on an encoded shaft, and the assembly is radially stepped to allow inspection of the disk at radial and angular positions while a microprocessor synchronized with the spinning disk collects light data to compile a map of surface reflectance. The polarization may be controlled to enhance image quality for different coatings and improve signal discrimination. Simple logic applied to point-by-point inequalities identifies the nature of physical changes responsible for observed effects. Polarization contrast and time difference contrast images allow visualization of defects and changes in substantially transparent layers well under a quarter wave thickness.

REFERENCE TO RELATED APPLICATION

This application is related to and claims the priority under 35 U.S.C.§119(e) of applicant's U.S. provisional patent application 60/000,611filed on Jun. 30, 1995.

BACKGROUND OF THE INVENTION

The present invention relates to measurements of light-transmissive thinfilms or layers of such films, and to measurements of surface topographyor detection of surface defects. It specifically relates to opticalmeasurement or detection, and to apparatus for performing such opticalmeasurement or detection of a thin film.

A number of common articles of manufacture now have constructionsinvolving thin films formed on relatively large area smooth substrates,and substrates wherein the underlying surface is reflective, possiblyconductive, and at least visually smooth if not optically flat. Todevelop manufacturing processes for reliably fabricating these articlesand to inspect them or understand the defects which arise in thesearticles, it is necessary to observe the thin films. These films may beliquid or solid, have a thickness substantially under one wavelength ofthe observation illumination, and may possess features or defects whichare observable only with meticulous methodology against the highlyreflective substrate, requiring a special probe. To detect changesoccurring on such a thin surface coating is an even more challengingtask.

In part, sensitivity of a probe is determined by devising a standardagainst which its measurements can be compared. Thus, for example, U.S.Pat. No. 4,873,430 describes a technique for measuring a thin film orsurface effect in which all reflected light is collected by anearly-contacting detector, and in which a certain degree of signalnormalization is achieved using separate detectors for specular anddiffuse light collection. A similar device has also been described in apaper of Meeks, Weresin and Rosen presented at the ASM/STLE TribologyConference, Maui, Hi. in Oct. 15-19, 1994. That system employs anintegrating sphere substantially contiguous with and tangent to a diskto capture all diffuse reflection from the disk surface; aperturesthrough the sphere allow two light paths to be directed at the tangentpoint for illumination of the point at 60° incidence and collection ofthe specular component reflected from that point. The device includesautomated scanning and collection, and autocalibration is achieved usingreference mirrors.

While each of these approaches utilizes sound theoretical models toaddress the problem of obtaining normalizable and meaningful levels ofsignal from a thin film, many practical realities should be recognizedin the operation of these devices. Thus, for example, the taking ofreflectance measurements on a micrometer-scale region may requiremultiply-repeated sampling and averaging, or integrating, to obtain arepeatable result. Furthermore, while it may be considerably moreinformative to compare like measurements taken from many consecutivepoints on a single disk, even the collection of many thousands of datasamples may still provide relatively sparse information about the totalworking surface of the disk. Furthermore, one of the more interestingavenues of research, involving wear test measurements taken from thesame disk before and after use, is severely hampered by the difficultyor impossibility of achieving submicron registration of the disk with anearlier position once it has been removed from the measurement stage.This restricts such tests to the brief wear testing that can beperformed while the disk remains on the optical measurement stage, or torelatively uninformative comparison of measurement ensembles, ratherthan pointwise measurement comparisons taken on a single disk over anextended time.

Accordingly, improvements in optical film measurement apparatus aredesirable.

SUMMARY OF THE INVENTION

Various problems described above are addressed and measurements of thinlubricant and protective film layers on a disk surface are reliablyachieved in an apparatus and method for measurement of surface coatingon a storage medium disk, comprising a disk support stage whichindependently rotates the disk while a probe support translates linearlywith respect to the disk orthogonally of the rotation axis. Acollimated, polarized light source provides a beam of polarized lightangularly-directed at a point in the plane of disk rotation, and a lightcollector, such as an integrating sphere with an input aperture largerthan the width of the beam and tilted with respect to the plane ofrotation, collects light from the illuminated point. The light collectoris positioned away from the disk to fully receiving the beam specularlyreflected from the disk and to detect the amount of polarized light soreceived, from which it determines a property of the fill layer.Properties measured by the device include thickness profile of thelayer, change of thickness or uniformity thereof, surface roughness, anddegradation or optical change of the layer material. The beam has a spotsize under about ten micrometers, and is directed at one or more layerseach of which is substantially under one micrometer thick. In oneembodiment, the source includes a laser diode which is temperaturestabilized to emit laser light at a single wavelength, and the diode isdriven by a current-controlled signal to produce a beam withsubstantially constant amplitude. This beam is shaped, collimated andpolarized to illuminate a circumferentially elongated spot on the disk.The collector is positioned with its collection aperture approximatelyone to five centimeters away from the disk, and is oriented to receivesubstantially only light that is specularly reflected from the disk. Awavelength or polarization filter may be positioned in front of thecollector to partially shield the detector output from ambient light andenhance the extinction ratio.

In this embodiment, temperature stabilization of the laser removeswavelength-dependent steering jumps in the optical path, whilestabilization of the diode electrical drive current removes backgroundamplitude changes, allowing detection of reflectance or absorbancechanges as low as 0.01 percent without requiring time-consumingprocesses such as averaging of multiple readings or performing lengthyintegrations. The method and apparatus produce fast and highly accuratesurface reflectance maps of the disk coating in radial coordinate R,disk rotation angle θ and polarization angle φ.

In a preferred embodiment, the device performs measurements on thesurface of a magnetic disk having a body and a multilayer structure setup to define magnetic storage domains in a thin subsurface magneticstorage layer. A surface lubricant layer coats the top, and a protectivecarbon planarizing layer lies below the lubricant, between the magneticstorage layer and the surface lubricant layer. The input illumination isdirected at an angle which lies between Brewster's angle of thelubricant and that of the carbon layer, and a processor controls thepolarizer, and a computer receives coordinating signals from the diskdrive and the probe transport to synchronize acquisition, i.e., todigitize and store detected light values as the stage moves through anarray of disk positions, thus compiling a map of disk reflectance at oneor more polarizations. In one embodiment a laser source is maintained ata substantially constant temperature by a Peltier device and is drivento produce a constant output intensity. The entire assembly operatesstably over a temperature range of at least 0 to 50° C., and isinsensitive to humidity so long as thermal cycling is conducted in sucha way that condensation does not occur. The apparatus operates in anenvironmental test chamber, and a disk may remain on the test stage andbe measured before, after and even during environmental testing.Comparison of the coordinates of a first acquired reflectance data mapwith a later acquired one resolves changes in thickness due to wear,evaporation or material redistribution. A simple logic table mayindicate the nature of physical process responsible for evolvingreflectances changes.

BRIEF DESCRIPTION OF DRAWINGS

These and other features of the invention will be understood from thedisclosure and claims presented herewith, together with the illustrativedrawings showing details of a representative embodiment, wherein

FIG. 1 shows a disk film optical measurement system in accordance withthe present invention;

FIG. 2A illustrates polarization and reflection events in the system ofFIG. 1; and

FIG. 3 shows a logic table for identifying physical changes formreflectance changes.

DETAILED DESCRIPTION

FIG. 1 illustrates a prototype embodiment 100 of the present invention,which includes a test stand or base 8 for holding a disk to be tested,and an optical measurement assembly 9 which is movably suspended on atrack or stage for one-dimensional translational movement along axis rover the base 8. Base 8 includes a motor driven turntable 11, e.g., aconventional so-called hard disk drive for rotating a magnetic mediastorage disk 10, (shown in phantom) as well as a magnetic head andcarrier of conventional type (not shown) for reading information fromand writing information onto the disk 10. Turntable 11 turns on a shaft(not shown) which has a 1024 position shaft encoder, and correspondingangular position signals corresponding to a shaft rotation angle s.sub.θappear on line 20, which connects via appropriate circuitry tosynchronize measurement acquisition in a processor, CPU 40. The positionsignals include a zero-position synchronization or framing signal,followed by the 2¹⁰ encoder signals in each rotation. The turntable may,for example, turn at 3,600 or 5,400 RPM, corresponding to sixty orninety thousand shaft encoder positions per second; if measurement speedis critical, a faster motor, a more finely divided shaft encoder, and/orspecial control chips may be used to interpolate sample positions orotherwise increase the number of data points per second.

Above the turntable 11, the movable optical measurement assembly 9 ismounted so that an illumination assembly 14 and a detection assembly 15are positioned and aligned symmetrically about a probe a point P in theplane of disk 10. Movement of the assembly stage 9 scans the point Pradially across the disk. Stage 9 is stepper controlled in onemicrometer increments, and position indicating and control signals arecontinuously monitored or controlled by CPU 40 on line 21, tosynchronize or coordinate the r, θ positions illuminated on the disk 10with optical results from the optical measurement assembly 14, 15, whichare provided to CPU 40, after suitable conditioning, along line 23.

In one embodiment of the optical measurement assembly 14, 15, theillumination assembly 14 includes a laser source 30 such as a fourmilliwatt Melles Griot 56DOL603 laser diode source producing a 670 nmoutput beam and an objective optical assembly 36 which focuses the laserbeam to a small spot on the disk 10. Preferably, a polarization beamsplitter 32 and a half-wave plate 34 are placed between the laser 30(which produces a polarized output beam) and the objective assembly 36,to clean up and more precisely control the polarization state of theillumination beam. The polarizer 32 passes light of a definedpolarization, while half wave plate 34 rotates the direction ofpolarization. Element 34 is a liquid crystal active half wave retarder,which may, for example, be controlled by the CPU, which provides a statecontrol signal on line S so that the illumination assembly automaticallyprovides either a selected s- or p-polarization state. The objectiveassembly 36 may be a simple but high quality, e.g., diffraction limited;focusing assembly, such as Melles Griot 06 GLC005, with a focal lengthof 48 mm. This produces approximately a six micron spot size from thelaser diode output at the surface of the disk 10.

With the above laser source, the output beam is non-circular, e.g.,about two by six millimeters, and the optics reduce the beam to aboutsix by twelve microns at focus. The source is positioned so the longdimension of beam cross-section is aligned circumferentially on thedisk. With illumination at 60° incidence, a circumferential extent ofabout fifteen microns is realized. As noted above, the stage 9 moves inone micrometer increments, so with this spot size the radial samplingdimensions overlap to assure full coverage by spots, of a disk in theradial direction. On the other hand, for a ninety-five millimeter disk,a 1024-position shaft encoder corresponds to a circumferential samplingdistance of several hundred micrometers, so that even with theasymmetric beam section there is relatively sparse sampling in thecircumferential direction. As noted above, when full area imaging isdesired, the data handling, positioning stage and/or softwareinterpolation/timing aspects are modified for greater resolution andspeed. In a preferred embodiment, the clock defined by the 1024 markshaft encoder is tied to a phase locked loop with a five-stage frequencydoubler so the angular position output signal is frequency-doubled fivetimes, providing a sample drive clock trigger at thirty-two times theencoder pulse frequency, i.e. 2¹⁵ pulses per revolution. This samplingfrequency provides full coverage of the entire disk, at the probe dotsize-resolution, in both radial as well as circumferential directions.

Within the laser assembly 30 a temperature sensor which is integral withor contiguous to the laser diode is used to develop control signals fora solid state Peltier effect cooler C that is energized to maintain thelaser cavity of the laser diode at a fixed temperature. This preventsthe laser output from jumping between cavity modes as the laseroperates. The laser is also operated at a constant output level. Suchoutput control may be achieved in several ways. For example, a beamsplitter, which also may be formed integrally with the laser diode (suchas by providing a partially transmissive, e.g., 0.01% transmissive, backface of the diode cavity) may provide a fixed portion of the output beamenergy to a photodetector to develop in a amplitude signal, which is fedin a negative feedback loop to the laser current drive, thus producing aconstant amplitude laser output. Alternatively, rather than sensing andcontrolling laser output, a simple constant-current driver may be used.In this case a simple current feedback circuit stabilizes the drivesignal level. With these two temperature and output stabilizingcontrols, the laser 30 produces a fixed wavelength output beam, with anamplitude that is constant to within one part in 10⁴.

The detection assembly 15 is mounted on the same stage or carriage aslaser 30, and is positioned at an equal angle of incidence over theradial path to receive the light beam specularly reflected from thepoint P on the disk as the carriage 9 moves along the direction r.

In a prototype embodiment, the collector assembly includes a small(e.g., one inch diameter) integrating sphere 16 having a one quarterinch aperture, with the aperture directed toward the sample positionpoint P and spaced about four centimeters therefrom. A baffled passageor other light shield may be used to shield the collector from lightother than that of the reflected beam, and for some protocols a fixed orvariable polarizer may be used to selectively pass a particular state ofpolarization, or a narrow bandpass interference filter may be used toprovide further discrimination of light collected by the sphere 16.These elements are indicated by element 18 at the collection aperture. Aphotodetector 17 is mounted onto the sphere to detect the level ofcollected light entering the sphere.

The integrating sphere 16 operates to smooth the amplitude of collectedlight over a dispersed area, so that the entire photoactive area of thephotodetector 17 receives collected light and any localized physicalvariations in the detector do not introduce variations in the detectoroutput. This is especially important since runout of the rotating diskcan cause the reflected beam to flit around to different points on adetector unless the light is first smoothed by the integrating sphere. Adiffuser may be substituted for the sphere.

Within the sphere a baffle (not shown) preferably shields the detector17 from receiving direct illumination through the collection aperture.Detector 17 is located at 90° to the light collection inlet, so arelatively small baffle may entirely shield the detector from directlight without significantly reducing the level of internally-reflectedcollected light.

Thus, the detector 17 at each point in time produces an outputindicative of the intensity of light reflected from point P.

The magnetic disk to be sampled may be of a standard commercial size,e.g., about sixty-five or ninety-five millimeters in diameter, and byway of example, may be formed of glass or of an aluminum/magnesiummaterial about 1.9 mm thick. On the surface of a representative disksubstrate are deposited a 10-15 micrometer thick nickel-phosphorouslayer, followed by a layer of chromium about one thousand Angstromsthick. The actual magnetic storage layer is then laid down as a 500Angstrom thick layer of a cobalt/platinum/chrome magnetic alloy medium.These layers form a totally reflective top of the disk.

A planarizing layer of carbon about 175 Angstroms thick is thendeposited over the magnetic storage layer, and a layer of lubricant,such as a perfluoropolyether with a thickness of about twenty Angstroms,is applied over the carbon layer. The disk itself is highly polished,and typically a narrow band of slightly roughened surface texture isprovided at a radially inward position to serve as a parking track onwhich the magnetic head may be brought to rest when not in use. Theroughened texture of the parking track prevents the head fromcontact-bonding or sticking to the lubricant when the disk is stopped.

A representative cycle of operation of the device proceeds as follows.Initially, the half-wave plate 34 is set to a default or unactuatedpolarizing state (s- or p-) to provide a light beam 50 having apolarization state P₁ at a level determined by the laser diode outputand polarizer 32. As the turntable 11 rotates, the optical assembly 9 ismoved radially to step through the radial extent of the disk, and theCPU stores digitized representations of the collected beam power foreach point specified by coordinates (r, θ) on the disk where 0≦θ<2π andr_(min) <r<r_(max), where r_(mnin) and r_(max) are the effective innerand outer diameters of the magnetic disk, for example from the parkingtrack described above to a band a few millimeters in from thecircumference. This data collection provides a quantitative record ormap of reflectance of all points on the disk for the given polarizationstate. The half-wave plate may then be energized to change thepolarization of beam 50 and compile a similar map at the same (r, θ)positions, with a different polarization. In the prototype embodiments,half-wave plate 34 is a liquid crystal plate, which is actuated with a0-5 volt signal to toggle between s- and p-polarizations.

The apparatus preferably resides within a closed environmental testchamber 60, provided with heaters and temperature control system 61,together with suitable means for forming or connecting to sources 62, 63of humidity, oxidant or other environmental agents which may beselectively actuated to expose the disk surface to a variety ofenvironmental test conditions. During such exposure, the disk drive isoperated in its normal fashion, and a magnetic head is carried acrossthe face of the disk over the lubricant layer, so various effects suchas frictional wear, lubricant erosion or redistribution, and the likeoccur.

In a further representative protocol, following operation under the testconditions, a second set of reflectance measurements are made to compilea second map, or a comparative reflectance map, of the same disk. Duringall this time, the disk preferably remains on the turntable so thatthere is an exact correspondence between the points with fixed (r, θ)coordinate in each data set stored by the CPU 40.

Thus, if surface reflectance maps are made with s- and p-polarizationsboth before and after testing, one has available information on both thechanges in s- and p-polarization reflectance, and the relative mounts ofs- and p-polarization reflection at each time.

As noted above, the beam 50 is directed at an angle φ of about 60°, andgenerally between about 53° and roughly 70°, so that tan (φ) liesbetween the index of refraction of the lubricant and that of the carbonlayer. By operating in a region where the light strikes above theBrewster's angle of one material (e.g., the lubricant) while being belowthe Brewster's angle for the other (the carbon layer) light of bothpolarizations will be represented in the collected light. Moreover, therelative amounts of detected s- and p-illumination, and the direction ofchange in intensity between two measurements can reveal the nature ofchanges in a simple logical array.

In general, the wavelength of the laser is not very important, since thelubricant film absorbs very little of the light at many availablewavelengths, while the carbon film does absorb, but with a typicalsensitivity which may be about 0.04% intensity change per Angstrom offilm thickness. By stabilizing the laser source as described above,applicant is able to repeatably detect such small changes in amplitude.The temperature stabilization not only enhances the intensity stability,but further assures that beam 50 remains relatively free of modehopping, so that diffractive jumps do not affect the aim; thus the (r,θ) coordinates taken at two different times will represent the samepoint P on the disk. The resolution of the reflectance map will ingeneral depend on the spot size of the lens and the accuracy of theencoder used to determine the location on the disk.

The above apparatus has the great advantage of being quantitativelyaccurate, and of having a "perfect memory" of disk coordinates when thedisk remains on the spindle. Typically about seventy per cent of thes-polarized light is reflected, while less than half of the p-polarizedlight is reflected. Operating against a substantially perfectlyreflective background, the total variation of intensity of the reflectedlight beam due to effects such as scattering, carbon thickness, andtexture variation and absorbance is only about two percent. However,with the aforesaid apparatus, variations of 0.1% are readily detected,and the reflectance range is readily expanded to enhance image contrast.The coordinate/intensity map has therefore been found to be quiteuseful. For example, a very high resolution map of lubricant thicknessis obtained by mapping the surface, rinsing the lubricant off, and thencompiling a second reflectance map and comparing the two maps pointwise.The CPU 40 may include software modules to determine a pointwisedifference map, to expand the range of detected intensity changes and toprint out a graphic image of the disk. It may also include patterndetection software to detect and to annotate specific features.

In addition, various enhanced measurement protocols may be implementedwith the basic embodiment described above.

FIG. 2A illustrates representative polarization-dependent beam effectsin the context of a carbon/lubricant two-layer magnetic disk coatingsystem. The top layer 10a of lubricant is only slightly absorptive, butis a dielectric and reflects a substantial portion of one polarizationat the given beam angle. The carbon layer 10b on the other hand isabsorptive, and absorbs up to about five to eight percent of lighttraversing that layer and reflected back off the underlying metalliclayers 10c. The collected beam 50' includes component beams 51, 52, 53from the various film surfaces that are enriched in one polarizationstate (beam 51) or depleted in amplitude (beam 53) or polarization state(beams 52, 53), as will be understood by those skilled in the art. Theprovision of polarization dependent reflectance maps greatly enhancesthe ability to probe the state of such coating layers.

The directional nature of the changes in s- and p-reflectance, and theabsorbance of the light of the beam component 53 reflected from theunderlying magnetic/metalized substrate 10c allow the small reflectancechanges occurring in the reflectance map to be interpreted in terms ofphysical processes or effects in the observed films. For example, byinspecting one radial track that has been wear tested and then observedin s- and p-light, a simple threshold discrimination between "light" and"dark" may be made either visually or by quantitative comparison to therecorded values in surrounding areas. FIG. 3 illustrates likely physicaleffects which in theory correspond to the four possible combinations ofrelative s- and p-image intensity.

As shown in the chart of FIG. 3, a track light in both s- andp-observation beams, corresponds to carbon wear. If light in s- but darkin p-, then there is lubricant removal. An image dark in s- and light inp-corresponds to a condition of lubricant build-up. Finally, if theobserved band appears dark in both polarizations, this may correspond toa number of changes, such as deposition of carbon, lubricant degradationand increased absorption, or the presence of scattering debris. Otherinterpretive meanings will be associated with particular disk images asdisk images are compiled and recognizable patterns emerge.

In addition to comparison of two polarization reflectance maps, beforeand after maps may be subtracted or processed to detect differences, asbriefly described above. Furthermore, the apparatus may be used atearlier stages of the disk manufacture to map reflectivity of one ormore of the lower coatings on the disk surface. For example, when thedisk is metalized with a layer of nickel and polished, the surface maybe reflectance mapped to identify each imperfection. These imperfectionsmay then be correlated with features in the later magnetic coating layeror with magnetic signal anomalies measured in the finished disk, toclarify the understanding of media variations and defects ordefect-causing traits.

The reflectance maps may also be used to characterize or adjustmanufacturing process steps. For example, inspection of the parkingtrack PT or measurement of the width of the transition zone between thetrack PT and the smoother recording surface may be used to adjustfabrication procedures used to form the roughened PT track, or toidentify spill-over effects that may impair performance. The performancevariation of different lubricants may also be readily observed, allowingquick evaluation of potential manufacturing materials.

The prototype embodiments described above utilized a 1024 position shaftencoder phase-locked to a frequency multiplier circuit for providing thedesired degree of resolution in the circumferential direction, with astepper-driven motor to carry the rigidly coupled optical illuminationand collection assembly over the disk such that the illumination spotfollows a radial path across the surface of the disk. The stepper wasdriven in increments of one micron, which was smaller than theillumination spot. However, the stepper could be actuated in incrementsof as little as one twenty-fifth of a micron, and the invention furthercontemplates such actuation in steps below one micron, when using, forexample, a smaller illumination spot, or when carrying out specializedprotocols such as higher resolution mapping of microdefects, orexploring problems of image alignment or signal variation such as whencorrelating image maps.

In general, for taking differential aging images, i.e., "before" and"after" data sets of a disk, it is preferred to collect a dense data setof substantially all r, θ, positions so that the corresponding points ofeach image are readily identified. However, when a point-by-pointquantitative comparison is not necessary, it is possible to compile amap of the disk surface at least an order of magnitude faster by runningthe radial stepper motor and rotational drive motors simultaneously andcollecting the reflection data along a spiraling path over the disksurface. This produces a high quality visual image of the entire surfacewhile sampling only a portion of its area. The spiral track data may beacquired in less than a minute, and may be used to quickly assess orsurvey the disc surface for a trait of interest, such as defect count ora regional pattern of wear or build-up.

Furthermore, while the acquisition of comparative measurements has beendescribed with reference to a turntable 11 having the disk 10 affixedthereto during at least two measurement cycles, the invention alsocontemplates systems and protocols wherein the disk is removed from themintable and is then later returned for a subsequent measurement. Inthat case, to compensate for the de-centering and rotational shift whichoccur between measurements, the CPU 40 (or a separate image analyzingprocessor) may include software for correlating two sets of collecteddata point observations, and determining a corresponding transformationbetween data sets to allow a differencing or comparison operation to beperformed on the two sets on a pointwise basis. Since the disk itself isrigid, once signal correlation has identified the differences in diskposition on the turntable, a simple transformation may be used to mapone data set to the other and allow pointwise data comparison and tocarry out image enhancement operations.

Thus, it will be seen that by providing a specific light source andcollecting specular reflection remote from the disk, and by smoothingthe collected light before detection away from the surface, a highlyinformative signal is obtained for evaluation of multiple layers of areflective surface. The invention being thus disclosed in respect of arepresentative embodiment, and measurement techniques being describedfor representative surface layers, further variations and modificationswill occur to those skilled in the art, and these are understood to bewithin the spirit and scope of the present invention and itsequivalents, as defined by the claims appended hereto.

What is claimed is:
 1. A method of evaluating at least one of lubricantcoating thickness and coating wear on magnetic media disks subject tovariable environmental and test conditions, such method comprising:A)providing a magnetic media disk includingi) a magnetic media layer, ii)a coating layer overlying said magnetic media layer, and iii) alubricant layer overlying said coating layer; B) supporting saidmagnetic media disk for rotation about a central axis extending normalto the substrate plane of said disk, and positioned for relativetranslation orthogonally of said axis with respect to a light source,said supporting being operable to selectively rotate said magnetic mediadisk about said axis as illumination is independently translated on saidrotating disk orthogonally of said axis; C) generating a collimatedlight beam with the light source displaced from said magnetic mediadisk; D) polarizing said collimated light beam emanating from said lightsource to provide polarized light; E) providing position indicatingmeans operable to determine a particular location on said disk uponwhich said polarized light impinges; F) providing an integrating spheredisplaced from said disk upon which said polarized light impinges, saidintegrating sphere havingi) a light receiving aperture having an axisinclined relative to said plane of said disk and a width larger thanwidth of said light beam so as to be operable to fully receive said beamfrom diverse, radially displaced light beam impingement locations onsaid disk, said aperture being generally axially intersected by thespecular polarized light reflected from said disk, and ii) lightintensity measuring means defined by at least a portion of the interiorof said integrating sphere; G) in a measurement with respect to saidparticular location on said disk, directing said polarized light againstsaid disk at said particular location and, during said measurement,i)reflecting said polarized light from said particular disk location,through said light receiving aperture of said integrating sphere, andinto the interior of said integrating sphere, and ii) measuring theamplitude of said polarized light impinging upon the interior of saidintegrating sphere during said measurement, and H) determining at leastone of wear of said coating layer and change in lubricant layerthickness at said particular disk location at least partially inresponse to said amplitude measurement.
 2. A method of evaluating in atleast one of lubricant coating thickness and coating wear on magneticmedia disks subject to variable environmental and test conditions, suchmethod comprising:A) providing a magnetic media disk includingi) amagnetic media layer, ii) a coating layer overlying said magnetic medialayer, and iii) a lubricant layer overlying said coating layer; B)supporting said magnetic media disk for rotation about a central axisextending normal to the substrate plane of said disk, and positioned forrelative translation orthogonally of said axis with respect to a lightsource, said supporting being operable to selectively rotate saidmagnetic media disk about said axis as illumination is independentlytranslated on said rotating disk orthogonally of said axis; C)generating a collimated light beam with the light source displaced fromsaid magnetic media disk; D) in response to changes in environmentaltemperature, modifying the temperature of said light source to maintaina generally constant temperature thereof and, operating at saidgenerally constant temperature, stabilizing said light source toi)maintain a constant intensity of light in said collimated light beam;and ii) maintain a constant wavelength of light in said collimated lightbeam; E) polarizing said collimated light beam emanating from saidtemperature stabilized light source to provide polarized light; F)providing position indicating means operable to determine a particularlocation on said disk upon which said polarized light impinges; G)providing a light collector displaced from said disk upon which saidpolarized light impinges, said light collector havingi) an effectivelight receiving aperture having a width larger than width of said lightbeam so as to be operable to fully receive said beam, and ii) lightintensity measuring means operative on received light; H) in ameasurement, with respect to said particular location on said disk,directing said polarized light against said disk at said particularlocation and, during said measurement,i) reflecting said polarized lightfrom said particular disk location, through said effective lightreceiving aperture of said light collector, and ii) measuring theamplitude of said received polarized light during said measurement; andI) determining at least one of wear of said coating layer and change inlubricant layer thickness at said particular disk location at leastpartially in response to said amplitude measurement.
 3. A method ofevaluating in at least one of lubricant coating thickness and coatingwear on magnetic media disks subject to variable environmental and testconditions, such method comprising:A) providing a magnetic media diskincludingi) a magnetic media layer, ii) a coating layer overlying saidmagnetic media layer, and iii) a lubricant layer overlying said coatinglayer; B) supporting said magnetic media disk for rotation about acentral axis extending normal to the substrate plane of said disk, andpositioned for relative translation orthogonally of said axis withrespect to a light source, said supporting being operable to selectivelyrotate said magnetic media disk about said axis as illumination isindependently translated on said rotating disk orthogonally of saidaxis; C) generating a collimated light beam with the light sourcedisplaced from said magnetic media disk; D) controlling a cooler tomaintain a generally constant temperature of said light source, andstabilizing said light source toi) maintain a constant intensity oflight in said collimated light beam, and ii) maintain a constantwavelength of light in said collimated light beam; E) polarizing saidcollimated light beam emanating from said temperature stabilized lightsource to selectively providei) p-polarized light, and ii) s-polarizedlight; F) providing position indicating means operable to determine aparticular location on said disk upon which said polarized andcollimated light beam impinges; G) providing an integrating spheredisplaced from said disk upon which said beam impinges, said integratingsphere havingi) a light receiving aperture having an axis inclinedrelative to said plane of said disk and a width larger than the width ofsaid light beam so as to be operable to fully receive said beam fromdiverse, radially displaced light beam impingement locations on saiddisk, said aperture being generally axially intersected by specularlyreflected light from said disk, and ii) light intensity measuring meansdefined by at least a portion of the interior of said integratingsphere; H) in a first measurement, and in respect to said particularlocation on said disk directing said polarized and collimated light beamagainst said disk at said particular location and, during said firstmeasurement,i) reflecting said light beam from said particular disklocation, through said light receiving aperture of said integratingsphere, and into the interior of said integrating sphere, and ii)independently measuring the amplitude of each of said p-polarized andsaid s-polarized light impinging upon the interior of said integratingsphere during said first measurement; I) subsequent to a period ofrotation of said disk and in a second measurement with respect to saidparticular location on said disk, directing said polarized andcollimated light beam again against said disk at said particularlocation and, during said second measurementi) reflecting said lightbeam from said first disk location, through said light receivingaperture of said integrating sphere, and into the interior of anintegrating sphere, and ii) independently measuring the amplitude ofeach of said p-polarized and said s-polarized light impinging upon theinterior of said integrating sphere during said second measurement; J)determining the difference in amplitude of each of said p-polarized andsaid s-polarized light increments impinging upon said interior of saidintegrating sphere during first and second measurements; and K)determining at least one of wear of said coating layer and change inlubricant layer thickness at said particular disk location in responseto at least one ofi) a difference in amplitude between said first andsecond measurements, of said p-polarized light impinging upon saidinterior of said integrating sphere; and ii) a difference in amplitudebetween said first and second measurements, of said s-polarized lightimpinging upon the interior of said integrating sphere.
 4. A method ofevaluating in at least one of lubricant coating thickness and coatingwear on magnetic media disks subject to variable environmental and testconditions, such method comprising:A) providing a magnetic media diskincludingi) a magnetic media layer, ii) a coating layer overlying saidmagnetic media layer, and iii) a lubricant layer overlying said coatinglayer; B) supporting said magnetic media disk for rotation about acentral axis extending normal to the substrate plane of said disk, andpositioned for relative translation orthogonally of said axis withrespect to a light source, said supporting being operable to selectivelyrotate said magnetic media disk about said axis as illumination isindependently translated on said rotating disk orthogonally of saidaxis; C) generating a collimated light beam with the light sourcedisplaced from said magnetic media disk; D) maintaining a generallyconstant temperature of said light source and stabilizing said lightsource toi) maintain a constant intensity of light in said collimatedlight beam, and ii) maintain a constant wavelength of light in saidcollimated light beam; E) polarizing said collimated light beamemanating from said temperature stabilized light source to providepolarized light; F) providing position indicating means operable todetermine a particular location on said disk upon which said polarizedlight impinges; G) providing an integrating sphere displaced from saiddisk upon which said polarized light impinges, said integrating spherehavingi) a light receiving aperture having an axis inclined relative tosaid plane of said disk and a width larger than the width of said lightbeam and operable to fully receive said beam from diverse, radiallydisplaced light beam impingement locations on said disk, said aperturebeing generally axially intersected by the specular polarized lightreflected from said disk, and ii) light intensity measuring meansdefined by at least a portion of the interior of said integratingsphere; H) in a measurement, with respect to said particular location onsaid disk, directing said polarized light against said disk at saidparticular location and, during said measurement,i) reflecting saidpolarized light from said particular disk location, through said lightreceiving aperture of said integrating sphere, and into the interior ofsaid integrating sphere, and ii) measuring the amplitude of saidpolarized light impinging upon the interior of said integrating sphereduring said measurement; and I) determining at least one of wear of saidcoating layer and change in lubricant layer thickness at said particulardisk location at least partially in response to said amplitudemeasurement.
 5. A method according to claim 4, wherein the step ofsupporting includes supporting on a turntable with an encoder to specifyangular position, and the step of providing position indicating meansincludes providing a controllably translatable assembly for moving saidlight beam across the disk such that angular position data of saidturntable and radial position data of said translatable assemblyidentify an illuminated position on the disk.
 6. A method according toclaim 5, further wherein the step of measuring includes compiling a dataset synchronized with said angular and radial position data of values oflight reflected from said disk at a plurality of spots substantiallycovering at least a region of the disk.
 7. A method according to claim6, wherein the plurality of spots lie on a spiral and cover only aportion of the disk.
 8. A method according to claim 6, wherein the spotslie on a plurality of parallel circumferential tracks.
 9. A methodaccording to claim 8, wherein the spots each have a dimension underapproximately ten micrometers and collectively cover substantially theentire surface of the disk.
 10. A method according to claim 9, whereinthe step of providing a controllably translatable assembly includesproviding a substantially rigid carriage directing the light source andthe aperture of said sphere at a common point, so that the lightreceiving aperture collects light specularly reflected from the commonpoint as motion of the carriage radially translates the common pointacross the disk.
 11. A method according to claim 6, further comprisingthe step of locating said turntable and translatable assembly in anenvironmental chamber to subject the disk to a controlled environmentalcondition prior to performing a measurement.
 12. Apparatus forevaluating at least one of lubricant coating thickness and coating wearon a magnetic media disk subject to variable environmental and testconditions, the magnetic media disk including i) a magnetic media layer,ii) a coating layer overlying said magnetic media layer, and iii) alubricant layer overlying said coating layer, and such apparatuscomprising:means for supporting said magnetic media disk for rotationabout a central axis extending normal to the substrate plane of saiddisk, and positioned for relative translation orthogonally of said axiswith respect to a light source, said means for supporting being operableto selectively rotate said magnetic media disk about said axis asillumination is independently translated on said rotating diskorthogonally of said axis; means for generating a collimated light beamwith the light source displaced from said magnetic media disk; means forpolarizing said collimated light beam emanating from said light sourceto provide polarized light; position indicating means for determining aparticular location on said disk upon which said polarized lightimpinges; an integrating sphere displaced from said disk upon which saidpolarized light impinges, said integrating sphere havingi) a lightreceiving aperture having an axis inclined relative to said plane ofsaid disk and a width larger than width of said light beam so as to beoperable to fully receive said beam from diverse, radially displacedlight beam impingement locations on said disk, said aperture beinggenerally axially intersected by the specular polarized light reflectedfrom said disk, and ii) light intensity measuring means defined by atleast a portion of the interior of said integrating sphere; means fordetermining a measurement with respect to said particular location onsaid disk by directing said polarized light against said disk at saidparticular location and, during said measurement,i) reflecting saidpolarized light from said particular disk location, through said lightreceiving aperture of said integrating sphere, and into the interior ofsaid integrating sphere, and ii) measuring the amplitude of saidpolarized light impinging upon the interior of said integrating sphereduring said measurement, said means for determining compiling a map ofdisk locations and detected amplitudes over said disk, said mapdetermining at least one of wear of said coating layer and change inlubricant layer thickness at said particular disk location at leastpartially in response to said amplitude measurement.
 13. Apparatus forevaluating at least one of lubricant coating thickness and coating wearon a magnetic media disk subject to variable environmental and testconditions, the magnetic media disk including i) a magnetic media layer,ii) a coating layer overlying said magnetic media layer, and iii) alubricant layer overlying said coating layer; wherein the apparatuscomprisesmeans for supporting said magnetic media disk for rotationabout a central axis extending normal to the substrate plane of saiddisk, and positioned for relative translation orthogonally of said axiswith respect to a light source, said supporting means being operable toselectively rotate said magnetic media disk about said axis asillumination is independently translated on said rotating diskorthogonally of said axis; means for generating a collimated light beamwith the light source displaced from said magnetic media disk; means forsensing temperature and modifying the temperature of said light sourceto maintain a generally constant temperature thereof and, operating atsaid generally constant temperature, means for stabilizing driving ofsaid light source toi) maintain a constant intensity of light in saidcollimated light beam; and ii) maintain a constant wavelength of lightin said collimated light beam; means for polarizing said collimatedlight beam emanating from said temperature stabilized light source toprovide polarized light; position indicating means operable to determinea particular location on said disk upon which said polarized lightimpinges; a light collector displaced from said disk upon which saidpolarized light impinges, said light collector havingi) an effectivelight receiving aperture having a width larger than width of said lightbeam so as to be operable to fully receive said beam, and ii) lightintensity measuring means operative on received light; means fordetermining a measurement, with respect to said particular location onsaid disk by directing said polarized light against said disk at saidparticular location and, during said measurement,i) reflecting saidpolarized light from said particular disk location, through saideffective light receiving aperture of said light collector, and ii)measuring the amplitude of said received polarized light during saidmeasurement; said means for determining compiling a map of disklocations and detected amplitudes over said disk for determining atleast one of wear of said coating layer and change in lubricant layerthickness at particular disk locations at least partially in response tosaid amplitude measurement.
 14. Apparatus according to claim 13, whereinthe means for supporting includes a turntable with an encoder to specifyangular position, and the position indicating means includes acontrollably translatable assembly for moving said light beam across thedisk such that angular position data of said turntable and radialposition data of said translatable assembly identify an illuminatedposition on the disk.
 15. Apparatus according to claim 14, furtherwherein the means for determining a measurement compiles a data setsynchronized with said angular and radial position data of values oflight reflected from said disk at a plurality of spots substantiallycovering at least a region of the disk.
 16. Apparatus according to claim15, wherein the plurality of spots lie on a spiral and cover only aportion of the disk.
 17. Apparatus according to claim 15, wherein thespots lie on a plurality of parallel circumferential tracks. 18.Apparatus according to claim 15, wherein the spots each have a dimensionunder approximately ten micrometers and collectively cover substantiallythe entire surface of the disk.
 19. Apparatus according to claim 14,wherein the controllably translatable assembly includes a substantiallyrigid carriage orienting the light beam and the aperture of said sphereat a common point, so that the effective light receiving aperturecollects light specularly reflected from the common point as motion ofthe carriage radially translates the common point across the disk. 20.Apparatus according to claim 13, further comprising an environmentalchamber surrounding said turntable and translatable assembly forsubjecting the disk to controlled environmental conditions prior toperforming a measurement.